class Solution {
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};
    bool vis[301][301];
    int m, n;
public:
    int numIslands(vector<vector<char>>& grid) {
        m = grid.size(), n = grid[0].size();
        int ret = 0;
        for(int i = 0; i < m; i++)
        {
            for(int j = 0; j < n; j++)
            {
                if(grid[i][j] == '1' && !vis[i][j])
                {
                    ret++;
                    bfs(grid, i, j);    // 把这块陆地全部标记一下
                }
            }
        }
        return ret;
    }

    void bfs(vector<vector<char>>& grid, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({i, j});
        vis[i][j] = true;   // 标记一下这块陆地已经遍历过了

        while(q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for(int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && !vis[x][y])
                {
                    q.push({x, y});
                    vis[x][y] = true;   // 标记一下这块陆地已经遍历过了
                }
            }
        }
    }
};